Fluvastatin, of which the full chemical name is R*,S*-(E)-(.+−.)-7-[3-(4-fluorophenyl)-1-(1-methyl-ethyl)-1H-indol-2-yl]-3,5-dihydroxy-6-heptenoic acid, as well as its sodium salt, are disclosed in EP-A-0 114 027. Fluvastatin is an inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase, which is a key enzyme in the regulation of cholesterol biosynthesis. Fluvastatin can be used pharmaceutically particularly as a hypercholesterolemic, hyperlipoproteinemic and antiatherosclerotic agent.
The present invention relates to a novel process for the preparation fluvastatin form A. Polymorphism is the existence of more than one crystal structure for a compound. Since properties can and do vary with crystal structure, polymorphism can influence many important properties of pharamceuticals: bioavailability, dissolution rate, compressibility, solubility, stability, filtering and drying characteristics etc. Different combination of experimental techniques (microscopy, variable temperature X-ray structure determination, spectroscopic and calorimetric methods) are used to discover, prepare, characterize, and study polymorphs of compounds of pharamceutical importance.
Many pharmaceutical materials exhibit polymorphism during heating and this refers to the generation of thermodynamically unstable melting forms. These polymorphic forms can be produced due to the given thermal history of the material. Different polymorphic forms can have differing solubilities and this can have a potentially major effect on the bioavailability of the drug when ingested. One polymorphic form may dissolve rapidly while another is very slow to dissolve. It is essential to screen pharmaceuticals for polymorphism for process optimization and for quality assurance purposes.
Fluvastatin sodium is specifically claimed as a substance in U.S. Pat. No. 5,354,772.
Polymorphic forms of Fluvastatin sodium are claimed in various patent applications viz. WO 97/49681, WO 02/36563 and WO 03/013512.
WO 97/49681 (equivalent U.S. Pat. No. 6,124,340 and EP 0 907 639) claims fluvastatin sodium crystalline form B. The PCT publication has compared properties of form B with form A. In accordance to WO 97/49681, the form A could be obtained by lyophilization process disclosed in U.S. Pat. No. 4,739,073. Several of these prior art process often result in a mixture of amorphous form and different crystalline form.
The present invention provides a robust process for the preparation of fluvastatin sodium in a amorphous form. The amorphous form of fluvastatin sodium thus prepared is substantially free from the anti-isomer.